1. Field of the Invention
This invention relates to an organic electroluminescent (EL) device, and more particularly, to a compound for use in a device of the type wherein an electric field is applied across a thin film of an organic compound to emit light.
2. Background Art
Organic electroluminescent (EL) devices include a thin film containing a luminescent organic compound interleaved between an electron injecting electrode and a hole injecting electrode. Electrons and holes are injected into the thin film where they are recombined to create excitons. Light is emitted by utilizing luminescence (phosphorescence or fluorescence) upon deactivation of excitons.
The organic EL devices are characterized by plane light emission at a high luminance of about 100 to 10,000 cd/m2 with a voltage of about 10 volts and light emission in a spectrum from blue to red color by a simple choice of the type of fluorescent material.
Doping is one technique for producing light emission of any desired color from organic EL devices. It was reported in Jpn. J. Appl. Phys., 10, 527 (1971) to change emission color from blue to green by doping anthracene crystals with a minor level of tetracene. With respect to organic thin film EL devices having a multilayer structure, it was reported in JP-A 63-264692 to incorporate in a host material having a light emitting function a minor amount of a fluorescent dye capable of emitting light different from that of the host material in response to light emission from the host material as a dopant to form a light emitting layer, thereby changing the color of light emission from green to orange or red.
With respect to long wavelength light emission of yellow to red, known light emitting materials or dopant materials include laser dyes capable of red oscillation (EPO 281381), compounds capable of exciplex emission (JP-A 2-255788), perylene compounds (JP-A 3-791), coumarin compounds (JP-A 3-792), dicyanomethylene compounds (JP-A 3-162481), thioxanthene compounds (JP-A 3-177486), mixtures of a conjugated polymer and an electron transporting compound (JP-A 6-73374), squalirium compounds (JP-A 6-93257), oxadiazole compounds (JP-A 6-136359), oxynate derivatives (JP-A 6-145146), and pyrene compounds (JP-A 6-240246).
It is reported in J. Am. Chem. Soc., 118, 2374-2379, 1996, that benzofluoranthene derivatives have a very high fluorescent quantum yield. JP-A 10-330295 and JP-A 11-233261 disclose organic EL devices having a light emitting layer in which a variety of host materials are doped with dibenzo[f,fxe2x80x2]diindeno[1,2,3-cd:1xe2x80x2,2xe2x80x2,3xe2x80x2-lm]perylene derivatives derived from benzofluoranthene.
Other light emitting materials disclosed heretofore include condensed polycyclic aromatic compounds (JP-A 5-32966 and 5-214334). Also dopant materials proposed heretofore include various condensed polycyclic aromatic compounds (JP-A 5-258859).
However, when these materials are used as the dopant, EL devices often fail to allow dopant molecules to exert their own fluorescence due to the interaction between dopants or between the dopant and the host.
Therefore, with respect to organic EL devices of the type in which a host material is doped with a fluorescent dye, a choice of host material is an important and difficult task in order for the device to produce high efficiency light emission. Currently available organic EL devices fail to reach a practically acceptable level of emission efficiency although fluorescent dyes having a high fluorescent quantum yield are used as the dopant.
When organic EL devices are fabricated using the doping technique, the energy transfer from host molecules in the excited state to the dopant is not 100%, and often not only the dopant, but also the host material emit light. Especially in the case of red light emitting devices, the chromatic purity is often exacerbated by faint light emission of the host material since the host material emits light in a wavelength region of higher visibility than the dopant. Further improvements in properties pertaining to the luminous lifetime and durability are needed, with the target placed on practical application.
An object of the invention is to provide an organic EL device capable of light emission to a satisfactory luminance, especially in a long wavelength region, and with a chromatic purity sufficient for use in full color displays, and having a sufficient durability to sustain such improved light emission performance over a long time.
The above and other objects are achieved by the invention which is defined below.
[1] An organic EL device comprising one or more organic layers between a pair of electrodes participating in at least a light emitting function,
at least one of the organic layers containing at least one of organic compounds having basic skeletons of the following formulas (I) to (IV) and at least one organic compound having a skeleton of the following formula (V) at the same time: 
xe2x80x83wherein Q1 to Q8 are independently hydrogen or substituted or unsubstituted alkyl, aryl, amino, heterocyclic or alkenyl radicals, 
xe2x80x83wherein R1, R2, R3 and R4 are independently aryl, fluorene, carbazolyl, alkyl, alkoxy, aryloxy, amino or halogen radicals, at least one of R1, R2, R3 and R4 is aryl, r1, r2, r3 and r4 each are 0 or an integer of 1 to 5, with the proviso that r1, r2, r3 and r4 are not 0 at the same time, R5 and R6 are independently alkyl, alkoxy, amino, aryl or halogen radicals and may be the same or different, r5 and r6 each are 0 or an integer of 1 to 4,
xe2x80x83wherein A101 is a monophenylanthryl or diphenylanthryl radical and may be the same or different, L is hydrogen, a single bond or an n-valent linkage, and n is an integer of 1 to 4,
Qnxe2x88x92L101xe2x80x83xe2x80x83(IV) 
xe2x80x83wherein Q is a pyrazinyl radical having fused thereto a six-membered aromatic ring containing 0 to 2 nitrogen atoms and may be the same or different, n is 2 or 3, and L101 is a single bond or n-valent radical, 
xe2x80x83wherein X1 to X10, L1 and L2 are independently hydrogen, halogen atoms, straight, branched or cyclic alkyl radicals which may have substituents, straight, branched or cyclic alkoxy radicals which may have substituents, straight, branched or cyclic alkylthio radicals which may have substituents, straight, branched or cyclic alkenyl radicals which may have substituents, straight, branched or cyclic alkenyloxy radicals which may have substituents, straight, branched or cyclic alkenylthio radicals which may have substituents, substituted or unsubstituted aralkyl radicals, substituted or unsubstituted aralkyloxy radicals, substituted or unsubstituted aralkylthio radicals, substituted or unsubstituted aryl radicals, substituted or unsubstituted aryloxy radicals, substituted or unsubstituted arylthio radicals, substituted or unsubstituted amino radicals, cyano, hydroxyl, xe2x80x94COOR1 radicals (wherein R1 is hydrogen, a substituted or unsubstituted straight, branched or cyclic alkyl radical, a substituted or unsubstituted straight, branched or cyclic alkenyl radical, a substituted or unsubstituted aralkyl radical or a substituted or unsubstituted aryl radical), xe2x80x94COR2 radicals (wherein R2 is hydrogen, a substituted or unsubstituted straight, branched or cyclic alkyl radical, a substituted or unsubstituted straight, branched or cyclic alkenyl radical, a substituted or unsubstituted aralkyl radical, a substituted or unsubstituted aryl radical or an amino radical), or xe2x80x94OCOR3 radicals (wherein R3 is a substituted or unsubstituted straight, branched or cyclic alkyl radical, a substituted or unsubstituted straight, branched or cyclic alkenyl radical, a substituted or unsubstituted aralkyl radical, or a substituted or unsubstituted aryl radical), or at least two adjoining radicals selected from X1 to X10, L1 and L2 may bond or fuse together to form a substituted or unsubstituted carbocyclic aliphatic ring, aromatic ring or fused aromatic ring with the carbon atoms to which they are attached, or L1 and L2 each may be a single bond. n is 1 or 2.
[2] The organic EL device of [1] wherein the at least one of the organic layers contains a host material and a dopant,
said host material comprises at least one compound selected from the organic compounds having basic skeletons of the formulas (I) to (IV) and
said dopant comprises at least one compound selected from the organic compounds having a skeleton of the formula (V).
[3] The organic EL device of [1] or [2] wherein in formula (V), at least two adjoining radicals selected from X1 to X10, L1 and L2 bond or fuse together to form a substituted or unsubstituted carbocyclic aliphatic ring, aromatic ring or fused aromatic ring with the carbon atoms to which they are attached.
[4] The organic EL device of any one of [1] to [3] wherein the compound of formula (V) is a compound of the following formula (VI): 
wherein X1 to X6, X9, X10, X11 to X16, X19 and X20 are independently hydrogen, halogen atoms, straight, branched or cyclic alkyl radicals which may have substituents, straight, branched or cyclic alkoxy radicals which may have substituents, straight, branched or cyclic alkylthio radicals which may have substituents, straight, branched or cyclic alkenyl radicals which may have substituents, straight, branched or cyclic alkenyloxy radicals which may have substituents, straight, branched or cyclic alkenylthio radicals which may have substituents, substituted or unsubstituted aralkyl radicals, substituted or unsubstituted aralkyloxy radicals, substituted or unsubstituted aralkylthio radicals, substituted or unsubstituted aryl radicals, substituted or unsubstituted aryloxy radicals, substituted or unsubstituted arylthio radicals, substituted or unsubstituted arylalkenyl radicals, substituted or unsubstituted alkenylaryl radicals, substituted or unsubstituted amino radicals, cyano, hydroxyl, xe2x80x94COOR1 radicals (wherein R1 is hydrogen, a substituted or unsubstituted straight, branched or cyclic alkyl radical, a substituted or unsubstituted straight, branched or cyclic alkenyl radical, a substituted or unsubstituted aralkyl radical or a substituted or unsubstituted aryl radical), xe2x80x94COR2 radicals (wherein R2 is hydrogen, a substituted or unsubstituted straight, branched or cyclic alkyl radical, a substituted or unsubstituted straight, branched or cyclic alkenyl radical, a substituted or unsubstituted aralkyl radical, a substituted or unsubstituted aryl radical or an amino radical), or xe2x80x94OCOR3 radicals (wherein R3 is a substituted or unsubstituted straight, branched or cyclic alkyl radical, a substituted or unsubstituted straight, branched or cyclic alkenyl radical, a substituted or unsubstituted aralkyl radical, or a substituted or unsubstituted aryl radical), or at least two adjoining radicals selected from X1 to X20 may bond together to form a substituted or unsubstituted carbocyclic aliphatic ring, aromatic ring or fused aromatic ring with the carbon atoms to which they are attached.
[5] The organic EL device of [4] wherein the compound of formula (VI) is a compound of the following formula (VIxe2x80x2): 
wherein X1 to X44 are as defined for X1 to X20 in formula (VI).
[6] The organic EL device of [4] or [5] wherein X1 to X20 in formula (VI) and X1 to X44 in formula (VIxe2x80x2) are independently substituted or unsubstituted aryl, alkyl, alkenyl, alkoxy or aryloxy radicals.
[7] The organic EL device of any one of [4] to [6] wherein at least one of X1 to X20 in formula (VI) and X1 to X44 in formula (VIxe2x80x2) is an ortho-substituted phenyl radical. [8] The organic EL device of any one of [4] to [7] wherein in formula (VI) or (VIxe2x80x2), either one or both of X1 and X4 and/or either one or both of X11 and X14 are ortho-substituted phenyl radicals.
[9] The organic EL device of any one of [1] to [8] wherein said at least one of the organic layers contains at least one organic compound having a basic skeleton of the formula (I).
[10] The organic EL device of any one of [1] to [9] wherein said at least one of the organic layers contains at least one organic compound having a basic skeleton of the formula (I) and at least one organic compound having a basic skeleton of the formula (II) at the same time.
[11] The organic EL device of any one of [4] to [10] wherein at least one of the organic compounds has a vibration structure in both an excitation spectrum and a fluorescence spectrum.
[12] The organic EL device of any one of [4] to [11] wherein at least one of the organic compounds has a Stokes shift of up to 0.1 eV.
[13] The organic EL device of any one of [4] to [12] wherein the host material in a light emitting layer has a greater electron affinity than an electron transporting layer and/or a hole transporting layer.
[14] The organic EL device of any one of [1] to [13] wherein the organic compound having a basic skeleton of the formula (I) is one wherein at least two of Q1 to Q8 are substituted or unsubstituted aryl radicals.
[15] The organic EL device of [14] wherein the organic compound having a basic skeleton of the formula (I) is one wherein at least six of Q1 to Q8 are substituted or unsubstituted aryl radicals.
[16] The organic EL device of [14] or [15] wherein the organic compound having a basic skeleton of the formula (I) is one wherein at least two of Q1, Q2, Q3 and Q4 are substituted or unsubstituted aryl radicals.
[17] The organic EL device of any one of [14] to [16] wherein the organic compound having a basic skeleton of the formula (I) is one wherein at least four of Q1, Q2, Q3 and Q4 are substituted or unsubstituted aryl radicals.
[18] The organic EL device of any one of [14] to [17] wherein at least two of the aryl radicals represented by Q1, Q2, Q3 and Q4 have aryl radicals substituted thereon.
[19] The organic EL device of any one of [2] to [18] wherein the at least one of the organic layers contains 80 to 99.9% by weight of the host material.
[20] An organic EL device wherein at least one of organic layers contains at least one organic compound having a basic skeleton of the formula (I) as set forth in [16] and at least one organic compound having a basic skeleton of the formula (IVxe2x80x2).
[21] The organic EL device of any one of [1] to [20], further comprising at least one hole injecting and transporting layer.
[22] The organic EL device of any one of [1] to [21], further comprising at least one electron injecting and transporting layer.
[23] An organic EL device comprising one or more organic layers between a pair of electrodes participating in at least a light emitting function, wherein the one or more organic layers contain organic compounds, at least one of which has a vibration structure in both an excitation spectrum and a fluorescence spectrum.
[24] An organic EL device comprising one or more organic layers between a pair of electrodes participating in at least a light emitting function, wherein the one or more organic layers contain organic compounds, at least one of which has a Stokes shift of up to 0.1 eV.
[25] The organic EL device of [24] wherein a host material in a light emitting layer has a greater electron affinity than an electron transporting layer and/or a hole transporting layer.